Frequency divider circuit



u y 1949- T K. H. DAVIS 2,477,047

I FR EQUENQY DIVIDER CIRCUIT I I P Fil ed Sept, 21, 1946 carpi/y -2o0v+2oov OUTPUT POTENTIAL AT POINT 4/ PO TE IV T/AL AT GRID 89 FIG. 2

POTENTIAL AT POINT 7/ POTENTIAL g 4T GRID 70 m/vE/v TOR K. H. DAV/5 a waA A T TORNE V Patented July 26, 1949 UNITED sir-Ares arEN-T FREQUENUYDIVIDER CIRCUIT Kingsbury H. DavisBernardsville, N. J., assignor. to.Bell. Telephone Laboratories, Incorporated, New York, N. Y'., acorporation of New York;

Application September 21, 1946, Serial No. 69.8;48-3:

Claims. 1-

This invention relates to electric wave generation, and, moreparticularly, to the translation of an electricwave: of one: frequencyinto one or more electric. waves of a" diflierent frequency orfrequencies.

Prior art circuits for this purpose have generally taken the form; ofself-oscillating or nonoscillating systems wherein a synchronizingtrigger pulse is imposed upon anexponentially rising control voltage;While these arrangements have successfully operated. inmanyapplications, there-have been numerous instances in which they,have-been ioundnot to be completely adequate for reliable service.

The self-oscillating. type of circuit, as. exemplified by themultivibrator, has a natural period of oscillationv and, at an time justpreceding that at which the circuit would naturally reverse, it presentsacritical period wherein it is particularly susceptible to voltagepulses that will cause premature reversals, This principle is employedin synchronizing these units, whereby the are caused to oscillate at ahigher frequency, or shorter period, than they would naturally attain.This controlled period is a combined function of the natural period 01'.the unit and the amplitude of the synchronizing: voltage pulse. Theeffect of variations in these factors is additive, that is, the naturalperiod may be increased by any amount and still there will be atheoretical pulse amplitude that will reverse the multivibrator at thecorrect time. This approaches the unsatisfactory limit of allowing notolerance in the amplitude of the pulse where thenatural period isallowed to vary to its limit and vice-versa. In practical design ofthese circuits, a compromise is made whereby both the pulse amplitudeand natural frequency are permitted some limited variation.

What has been said regarding the effect of pulse variations in' theself-oscillating circuits is equally true in non-oscillating systems inwhich synchronizing pulses are impressed upon an exponentially risingvoltage of a control electrode. As the rising voltage approaches thecutoff point of the trigger circuit, there exists a critical periodduring which small "stray voltages may cause premature tripping of theunit, or where amplitude variations between successive control pulsesmay cause erroneous operation. It is obvious that, as the "operatingfrequency is increased, or as the step-down ratio is increased, agreater number of synchronizing pulses are impressed upon the unit pertime interval. As this number increases, the amounts by which the pulseamplitude and the natural frequency may vary from optimum values withoutcausing loss.

divider which will not. support. salt-oscillations,

but which stands by indefinitely in an attending position until thesynchronizing. signal is received.

A still further object 1 tqprovide. a, circuit.- for frequency reductionwork in which reasonably expectable variationsin the. amplitude of the.2 .1 trolling pulse. arenotoperatively etlective.

Other objects and advantages will become apparent from the followingdescription of one preferred embodiment, when considered with. ref.-erence to the drawingl in wh ch;

Fig. 1 represents schematically the arrangement of a frequency dividingcircuit in accordance. with the present invention; and

Fig. 2 illustrates biasing potentials and. super-. posed controlvoltage. pulses for one. operating cycle of the frequency divider ofFig. 1..

As shown in schematic form in ig. l, the ire: quency dividingarrangement comprises two sub: stantially equivalent portions. Eachportion performs a holding and a operation. The holding tubes 43 and 5.5are so disposed that. when one is saturated the other tube is out. off.This is a stable condition and, in the absence of any control voltages,it will persist. The timing tubes. it or on are arranged to be cut on bythe anode voltage drop accompanying saturation of the. as.- sociatedholding tube. When one of the timing tubes is so cut off, it immediatelyapplies a high positive voltage to the control electrode of itsassociated holding tube and effectively raises the potential of thiselectrode beyond the efiective range of any reasonably expectablecontrol pulse. Variations in the potential atthe anodes 44 and of theholding tubes 43 and 55 are madev available at output terminals 12 and I3. r i

The circuit departs from the conventional multivibrator in that. it willnot sustain self-oscillations, but, at a predetermined time after thetiming tube assumes control of the holding tubes control electrode, itrelinquishes this control, and conditions the holding tube iorreversalby the next succeeding control pulse. If no control pulse isforthcoming, the circuit remains in a ready or stand-by condition.

The timing tubes 48 and 60 use conventional resistor-capacitor chargingarrangements 45, '41 and 58, 59, the values of the components of whichare chosen in the usual well-known manner. By a proper choice of thesevalues, the timing tubes render the holding tubes 43 and 55 unresponsiveto control pulsesfor any desired number of pulses. The timingarrangementdifiers somewhat from that used in the "conventionalmultivibrator, since in this arrangement the timing tube saturates.one-half period of the controlling frequency be fore the frequencydivider is to be reversed,'in stead of one-half period of the.controlling frequency after the desired reversal time, as is done p inthe conventional controlled inultivibratorn Accordinglydor odd ratios ofstep dow'n, the nat ural period should be arranged s'o'thatt'h'e timing1 tube, 48 or 6B, saturates at 1'-1/2 periods of the controllingfrequency after its control electrode has been driven negative, where ris equivalent to the'step-down' ratio, In thecase of even ratios ofstep-dowmthe 'timingjoi the two sides will difierin the same inanner,and foressentially the variations in the control pulse amplitude it-isnecessary to "effectively carry the control electrodes ,well past'cut-oii and saturationrpoints. Because grid, current starts as'soon as thecontrol grid electrode exceedsjzero, bias it is difficult to raise thiselectrodepotentialihighly positive. ,To

'4 opposition, are applied through coupling condensers 65 and 66 to theholding tube control electrodes B1 and 68. Assume at time A (Fig. 2),that tube 43 is saturated, and that timing tube 48'has only recentlychanged from a non-conduction to a saturated condition. Thecomplementary holding tube 55 is cut off and its timing tube 60 isapproachingthe end of its saturated point 4|. The potential at point 4|drops below period. Negative "control pulse 151s impressed through thecoupling condenser 66 to the biasing I, the:va1ue correspondingv toout-off potential at the controlelectrode 68, and there is an attendingvoltage increase at the anode 44. This increase istransferred by way ofcapacitor 45 to I the saturatedcontrol electrode 69 where'it apresistor5|, increases the potentialat point "H reduces the potential at theanode56. Thesudden change in this anode potential-is communi-f cated tothe timing tube 60, by way'of the timing- '1 pearsas an ineffectivepositive pulse 16.

This anode voltage increase also, by way of coupling to a level 11,which level exceeds the saturation voltage for the control electrode161' and. greatly circuit capacitor 58, to drive the control electrode10 to a highnegative potential ll! andcut off the timing-tubeto. The-timing circuit, comprising capacitor 58 and*resistor .59, beingreturned to the supply of'positive potential, starts charging towardthat value essentially as a linear function, and accurately'measures'the cut-toil period of the timing tube 60. The concurrent risein voltage attheanode 6| is fed'back byway of resistor 63 to the biasingpoint 1|, tov carry this point to a high positive voltage level '18,.Con-' trol electrode 61 is also'carried positive and draws current.Because of the'voltage drop across the,

large decoupling resistor.54,:-iniitscurrent conpermit what efiectivelyamounts to carrying the grid electrode to a hi gh positivepotential, rela tively high valuedecoupling'resistors 42 and 54 areinserted in the "grid'circuit between the electrode proper and itsbiasing point 4| or II. Biasing points Aland Tl arejunction points onthe voltage divider circuits comprisingresistor 53 in series,withparallel resistors,5|, 63 and resistor in series with the parallelresistors 52 and 54.

One end ofleach divideris connected to constant,

negative potential.,., The potentials at points ii and 4|, increase ordecrease substantiallyin unisonwiththe changesin positive voltagesupplied at the anodes v44 6| and 5.0, 56, respectively. By a suitablechoice of; divider resistor values, the potential at .thesepoints, andII, may be made sufliciently positive to permit large variations in thecontrol pulse amplitudewithout causing preure rer s s.,v

, In'reierrinstq F it. shouldbe noted that.

the, first a thirddiagramsshow the potential atthebiasing points 4| and'llrespectively, while the second and vfourth diagrams displaypotentials at the control electrodes wand 10, Potentials at the biasingpoints 4| and ll, rather than attheiassociated control electrodes 68 and51, are shown in order to demonstrate more clearly the large p otentia lvariation that may be permitted at these biasingpoints without affectingthe circ it operation;

V 'With rerien eto' th circuitarrangement "of 'Fig. 1 and the controlv'oltage diagrams of Fi'g. 2,

consider the operation of the 'circuit whennegatlve control voltagewaves I70 and H, in phase duction path,the control electrode'ilil'willassume a potential" level slightly in excess of, zerofor all potentialsexceeding-zero at the biasing point'll. The high positive potentialatpoint 1| renders the control electrode :61 iinsens'itivegto thesucceeding negative controlpulsesflil'y This condition willmaintain'until the control electrode Ill;

, again acquires "sufiicientpositivebias to permit conduction in thetiming tube' 60 which occurs at time B. In addition'to negativelycharging j the timing circuit58, 59, the decreased potential at theanode 56' holds, by way-of the resistor 52,'[ l the potential of biasingpoint 4| at a high mega j tive potential 18f." no current is flowing,the control electrode 68 assumes thishigh negative stray positive pulses(noneshown);

potential; and is insensitive to negative control pulses l9 and tdanyreasonably expectable At time B,'the-'timing"circuit 58, Wins charged toa potential that corresponds to the cut-off potential at the grid 10 ofthe timing tube :6 0, and'current 'conductionis started therein.

The grid potential continues increasing tozero potential and current.saturation iat point 8|.

simultaneously, the"decreasingwanode potential at the anode 6| decreasesthe voltage across the sufiicient to affect the potential at the controlvoltage dividerfcirc'uit containing resistor 63 andreduces the"potential at the biasing'point 1|; The po'tentialatthebiasing point'llis reduced to the near zero level 8| which dropis; not

electrode 61, but does'place this electrode in a position tobeiireduced. below cut-off :potential by the next succeeding :negativecontrol pulse V 821 thatis received at point II.

"At time 90, the negative control. pulse 82' momentarily cuts oil".holding tube 55; and gives 7 there.

risetoahigh-positive voltage pulse at its anode 56.

This positive pulsejby wayof resistor 52, carries the potential at thebiasing point M to positive level '83, which is sufficient to saturatethe holding tube 43-anddecrease the potential at its anode -44. In themannerpreviously described when-the 'level 85. In this condition, thenegative control pulses '85 are ineffective in controlling the potentialof-the control electrode 68. The negative control pulses 86'have noeffect upon the control electrode-61 as it has-assumed the high negativepotential of its biasingpoint 1 I. These conditions will exist until thetiming tube 48 again becomes conductive, at time D, and prepares thecircuit for another reversal at time E in the manner previouslydescribed.

It should be noted that, at times .C" or E, if no control pulse isreceived, the circuit is not reversed 'but maintains its stability andassumes a ready position until a reversing pulse is received. Thischaracteristic is of considerable value'in a frequency dividingarrangement wherein it is desired that no output be produced if thesynchronizing control pulses are interrupted.

Although in the foregoing description, the control waves l and H wereassumed to comprise only negative pulses this condition is notnecessarily controlling. It should be appreciated that these controlwaves may include both positive and negative pulses. If positive pulsesare included it is possible that, in case of unfavorable voltagephasings, the observed operating margins may be slightly less favorablethan in the described embodiment.

Although this invention has been described with reference to a specificapplication, and specific circuit constants have been shown by way ofexample, it should be understood that it is not to be considered aslimited thereto, since other applications thereof, not departing fromthe spirit and scope of the invention will readily occur to thoseskilled in the art to which the invention pertains.

What is claimed is:

1. A frequency divider circuit in which reversals in response tocontrolling synchronizing pulses are substantially independent ofvariations in the amplitude of said pulses, said circuit comprising aplurality of space discharge devices, each having an anode, a cathode,and at least one control grid element, and control grid-cathode andanode-cathode circuit therefor, each of said anode-cathode circuitsincluding a source of positive potential resistively connected to theanode thereof, two of said discharge devices operating as holding means,and two other of said discharge devices operating as timing means, eachof said holding means having an impedance connection between its anodeand the control grid element of said other holding means, the anode ofeach of said holding means being connected througa capacitive circuit tothe control grid element of a said timing means, each of said timingmeans having its anode resistively connected to the control grid elementof its associated holding means, said last mentioned control gridelements being "resistively connected to asource of negative potential,and said control grid "elements of tsaid timing :means being resistivelyconnected to a source of positive potential, terminal connection meansfor supplying said controlling synchronizing pulses-to the control gridelements of said holding means, whereby, upon receipt of a negativesynchronizing control pulse by one holding 'means, said one holdingmeans is 'rendered'insensitive to succeeding negative synchronizingcontrol pulses, and said other holding meansiis rendered responsive tosaid negative synchronizing control pulse next succeeding apredetermined number of said succeeding control pulses.

'2. A frequency dividing circuit comprising a plurality of electrondischarge devices, each of said-devices including atleast a cathode, .ananode and a control grid electrode, control grid-cathode circuits andanode-cathode circuits therefor, said anode-cathode circuits comprisinga source of positive potential resistively connected to said anodes,input terminal means connected to the control grid electrodes of two ofsaid devices to supply thereto electric control waves of the frequencyto be divided, resistive means interconnecting the control gridelectrode of each .of

two of said devices with the anode electrode of the other of saidtwo'devices, and means for controlling the potential of said controlgrid electrodes whereby said devices are "alternately 'responsive tosaid supplied control 'waves, .sa'id icontrol means com-prising anothertwo of said electron discharge devices, each of said last mentioneddevices having its control grid electrode connected to a source ofpositive potential through a direct current conductive path, having thesame electrode connected through an impedance path to the anode of oneof said first-mentioned two electron discharge devices, and having itsanode connected through a direct current conductive path to the controlgrid electrode of the same first-mentioned device with which its controlgrid electrode is associated.

3. In combination, in a frequency dividing circuit comprising twosubstantially equivalent complementary portions, each of said portionscomprisin a first and a second electron discharge device, each suchdevice comprising an anode, a cathode and at least one interposedcontrol grid element, control grid-cathode circuits and anodecathodecircuits therefor, said anode-cathode circuits comprising a source ofpositive potential resistively connected to said anodes, the anode ofeach of said first devices being connected through an impedance path tothe control grid element of said other first electron device whereby thecontrol element potential of each of said first devices varies as theanode potential of each of said other first device is varied, each ofsaid first discharge devices being interconnected to one of said seconddischarge devices by a time-constant circuit connecting the anode ofsaid first device to the control grid element of its associated seconddevice, and by an impedance path between the anode of said second deviceand the control grid element of said first device, whereby the potentialof said control grid element of said first device is held positive withrespect to its cathode whenever its associated second discharge deviceis rendered non-conductive.

4. A frequency dividing circuit comprising a plurality of electrondischarge devices, each of said devices including an anode, a cathodeand at least one control grid element, control gridcathode circuits andanode-cathode circuits therefonsaid anode-cathode circuits comprising asource of positive potential resistively connected to said anodes, twoof said devices each having its control grid element interconnected withthe anode of the other of the said two devices and having input terminalmeans connected to the control element whereby control electric waves ofthe frequency to be divided are suppliedto the control elements of saidtwo devices, means for controlling the potential of said controlelements whereby said discharge devices are alternately made responsiveto said control electric waves,

:said means comprising two additional of said electron discharge deviceseach having its anode and control grid element connected by separateconductive paths to the control grid element and anode, respectively, ofone of said first-mentioned two devices, whereby the potential of thecontrol element of each-of said first-mentioned devices varies directlyas the potential of the connected anode of one of said additionalelectron devices.

' 5.'A signal wave frequency dividing system comprising two conjugatecircuit branches, each of said branches comprising a holding electrondischarge device and a complementary timing electron discharge deviceincluding anode, cathode and control grid electrodes, anode-cathodecircuits and control grid-cathode circuits therefor, each of saidanode-cathode circuits compris- I ing a source of positive anodepotential and an anode load impedance in series connection, separatesignal input means connected toeach of said holding electron dischargedevices, an impedance coupling circuit interconnecting the anode of eachof said holding devices and the control grid of its complementary timingdevice, each of said coupling circuits possessing a time-constantcharacteristic that exceeds the period of the signal wave the frequencyof which is to be divided,

' means for rendering each of said holding devices insensitive to inputsignal waves during the inter- REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS Number 7 Name Date- 2,289,987 Norton July 14, 19422,289,988 Norton July 14:, 1942 2,304,813 Gibbs Dec. 15, 1942

